Motion during an MRI examination can seriously compromise image quality. In a typical examination, multiple scans are performed. The geometry of these scans is planned on a survey scan which is one of the first scans that is performed. If the patient moves after the acquisition of the survey scan, the scanned location is different from the planned location throughout the following part of the examination. This may lead to a bad image quality due to motion artifacts or a wrong anatomy which is imaged. As a consequence the total time of the examination is prolonged because scans need to be repeated.
T. Nielsen et al., Proc. ISMRM, p. 2472 (2012) discloses a method for rigid inter-scan motion compensation in neurological exams.